Ram-type blowout preventers are used to close the upper end of a well bore to maintain the well under control whenever there is danger of a blowout. The rams move in guideways in the body of the blowout preventer and when closed are positioned to seal across the bore through the body with a ram front packer. To make the seal complete a sealing element is provided between the ram and the ram guideways, usually across the top and side of the ram extending from the ram front packer. The operation of the rams causes wear particularly in the lower surface of the guideway, and excessive wear can reposition the ram so that a leak can occur across the ram top sealing element.
U.S. Pat. No. 3,692,316 discloses a ram-type blowout preventer with keys secured to the underside of the rams sliding in slots in the bottom of the guideways to maintain the rams in proper alignment but there is no suggestion of compensating for wear.
U.S. Pat. No. 1,970,964 discloses a well flow stopper which includes a plate that is moved across the bore and includes an upper packer and a pair of lower springs to support the plate and urge it upward with the aid of pressure to sealed position. U.S. Pat. No. 1,981,279 discloses a ram type blowout preventer including a spring-pressed ring to hold the rams against the upper seat. The use of springs as shown in these two patents would not be effective to compensate for excessive wear in guideways and/or ram lower surface, particularly when the string passing therethrough is hung in tension on the ram.